Ocean acidification

Our oceans are absorbing about one-third of the carbon dioxide in the atmosphere. As a result, they are becoming more acidic. Associate Professor Abby Smith, from the University of Otago, is researching the role that bryozoans can play in monitoring these changes in pH.

Point of interest Discuss what is meant by the term ‘canary in the coal mine’.

Transcript

Associate Professor Abby Smith

People have been pumping carbon into the atmosphere for a long time. They do that by burning things that have carbon in them and the carbon goes into the atmosphere, and that would be just no problem except that obviously the carbon dioxide is acting as a greenhouse gas and causing problems with climate change. One of the things climate change people are happy about is that the ocean absorbs carbon from the atmosphere, so CO2 is sucked up from the atmosphere into the ocean. A good third of what we produce is being vacuumed up by the oceans, which is terrific, only it’s not so good for the oceans. When the oceans absorb carbon dioxide it changes their chemistry a little. It drives a carbon cycle, which involves a series of fairly simple chemical equations, and it causes the pH of the sea to go down. That means the sea becomes a little more acidic. Now, if we were only producing a little bit of carbon, then the ocean might only become a little more acidic and that would be OK, but we are producing enormous amounts of carbon, and the ocean is absorbing more carbon more quickly than it ever has ever in the past, and it is changing in terms of its pH very, very rapidly, and critters living in the water just can’t adjust to that. So we have organisms that are making calcium carbonate skeletons – what they need is to have a certain pH, and when it gets too low, they can’t do it any more. The pH of the oceans before people started messing around with the atmosphere was about 8.2. It’s currently about 8.1. Doesn’t seem like a big jump, but it’s on a logarithmic scale, and it is a big jump. And we estimate that with another 0.4 – which would be down to 7.7 – you could pretty much finish off calcification in the ocean. Really, most organisms would find it too difficult to calcify under those circumstances. And we also estimate that, if we keep pumping out carbon dioxide at the speed we do, we could easily reach that threshold by the end of the century. Bryozoans have the potential to be ‘canaries’, to show us when acidification is starting to attack certain types of ecosystems. But also they have the opportunity to be kind of like a giant monitoring system, because we have these – in the Southern Hemisphere – these continental shelves that are covered with bryozoan material from 30 metres water depth out to 120 metres water depth, and if ocean acidification is occurring at different water depths, in different ways – hey, it’s creeping up the shelf or say it’s creeping down the shelf, and we are not really sure what we think it’s going to do – you would be able to tell where it was attacking by looking at these materials.